Aluminum Composite to Lower Weight in Brake Rotor

The research team is developing a one-piece brake rotor that will be made of a single material that is both lightweight and extremely durable. The team will replace the traditional cast-iron rotor material with an aluminum alloy designed for high-temperature operation. The alloy is reinforced with ceramic particles and fibers that are functionally graded to create a material whose properties can be customized in each section of the rotor.

"These functionally graded materials allow us to create the optimal composition for each part of the rotor," Gupta said in an NYU-Poly press release. "The hybrid material allows us to provide reinforcement where additional strength is needed, increase high-temperature performance, and minimize stress at the interfaces between the zones. Together, this should boost rotor life significantly, reducing warranty and replacement costs, and the weight savings will improve the vehicle’s fuel efficiency."

Gupta and the research team expect to have a functional rotor prototype within 12 months.

Cool development and yet another tool for auto makers to take weight out of their vehicles, aiding in energy efficiency and potentially, reducing costs. With all the focus on EV battery weight and other aspects of the next-generation of more fuel efficient cars, it's great to get a handle on some of the other developments and research around materials that can also aid in promoting more efficient vehicles.

This sounds good, but break systems in general need to be redesigned. The current problem with breaks is that the break pads are essentially in contact with the disk at all times. All the cars and motorcycles I've had, the rotor is never free to spin by hand without hearing the pads rubbing against the disk. I understand that it gives quicker response to stop the closer the pads are, but imagine how much mpg and rotor/pad life is robbed by the current design. Imagine riding your bicycle with the break pads rubbing all the time. When we have so much horsepower available, we tend to ignore the obvious little inefficiencies.From what I've read, I like what Tesla did with their brakes...zero binding when not breaking!

I can't wait to see a $500 brake rotor for a $10,000 car. Materials will be 10% of the vehicles value. Can you picture this repair on a 5 year old chevy cavalier or equvalent vehicle? lol, I can't...

There comes a point where practicality and reality need to mix. Cna this be done, sure, but when I can go out and purchase an $80 brake rotor for a 1 ton truck, and instal it myself, I shudder to think what this new material would cost.

Remember when plastic bumpers were supposed to make cars cheaper? yeah... now it costs over $1k to get the stupid thing repainted when some jerk dings you up in a parking lot, where the metal one didn't show the mark in the first place.

Neat idea, but until it's economically feasible, it's a waste of time... much like EV's without gov't subsidation (which still comes from our pocket).

@kleetus: I agree with you about cost -- at least for the time being. When I worked on aluminum MMC brakes, it was for military applications, where cost vs. weight considerations are very different than in the civilian market. But a lot of work is being done to find cost-effective ways of producing these materials.

By the way, there is no such thing as a 5-year-old Chevy Cavalier, since 2005 was the last model year for Cavalier. My Chevy Cobalt -- the model which replaced Cavalier -- is more than five years old.

@Dave Palmer: Lol... okay, maybe I'm dating myself with a cavalier, but your cobalt would be the same premise. A lower cost vehicle with a significant repair bill for normally wearable items.

Now having the price come down over time I can certainly believe, just look at cmputers, but there are a number of other items, like 'lubed for life' suspension components and u-joints that never lived up to the name, and were just as expensive if not more based on their novel idea that they are 'better'.

Ann, Great story. The possibility of a 3x service life is obviously a huge advantage and balances off against the higher initial cost and makes determining the value more interesting. Any specific interest among industry partners for this technology? Manufacturability and ability to scale to achieve target costs have to be a major objectives.

The best part is the weight reduction is unsprung weight, so has the potential to improve handling and ride quality as well as improve fuel economy and hard braking performance.

Logical place to start would be w/ performance/luxury brands/models, where the higher initial cost is better tolerated, then move down into lower priced/featured vehicle lines as high volume real world experience accumulates, much as (long long ago now) front disc brakes, then, more recently, rear, have replaced drums.

Thanks for the comments and feedback. Beth, I was also pleased to see an area of the vehicle besides batteries and body panels targeted for weight reduction. Al, this is still in R&D--the prototype isn't yet completed--and there was no mention yet of any industry partners. I, too, was impressed by the 3x service life improvement--I hope it turns out to be true. Stephen, thanks for the info about unsprung weight. And I agree, it's most likely that this, like many other automotive material innovations, may be aimed at higher-priced vehicles.

Does anyone know why Carbon brakes are not getting cheaper? After all carbon isn't that expensive a feedstock. How are they made?

They would be much lighter than even this advance with the lower weight advantages in handling and mileage.

Some brakes come with retracting clip springs that pull the pads off the rotor. In every EV I do I always check the brakes and many other drags like diff fluids, new low rolling resitance tires, aero mods, etc which can literally increase range 10-50%!! Or cut the battery pack/cost/weight as much for the same range.

Of course the best brake is one that doesn't have to stop all that excess weight most cars have by designing in lightness, KIS.

@Ann: Thanks for a good article about an issue which is very close to my heart. I used to work for a brake manufacturer, and heavily promoted the use of metal matrix composites for both rotors and calipers. As your article points out, this is an area where significant weight savings can be achieved. Many companies are doing work in this area. One which comes to mind is GS Engineering.

It may be worth noting that cast iron itself can be thought of as a composite material (with graphite as the reinforcement), and that induction hardening can provide "functionally graded" properties. In that sense, functionally graded metal matrix composites are not really such an exotic departure from what brake manufacturers have been doing for years -- we just never called it that. But aluminum MMC technology gives us an even greater ability to tailor material properties, at a fraction of the weight.

It would be very interesting to know some of the details of this product. For example, what is the reinforcement? (Silicon carbide, aluminum oxide, both, or neither?) Is the composite made by stir casting or infiltration? How is the distribution of the reinforcing particles/fibers achieved? Of course, REL might be understandably reticent about revealing all of these details.

A major issue with MMCs, not mentioned in the article, is machinability. Putting hard ceramic particles or fibers in a material is a great way to improve its mechanical properties. But how do you machine something which is full of chunks of hard ceramic without destroying your tooling? You either have to use expensive diamond tooling, or you have to find an ingenious way to keep ceramic out of the areas you want to machine.

One interesting approach for brake calipers, which Allied Signal took out a patent on back in the '90s, is to cast an aluminum MMC with unreinforced aluminum inserts. The inserts go in the areas which are going to be machined later.

I could go on and on about this. Thanks for an article on such an important topic!

Thanks, Dave, I was hoping you'd weigh in with some info and feedback about metal matrix composite (MMC) technology. Thanks also for the links. I'm especially interested in what you said about machinability. In fact, when I first read about this MMC I wondered how the heck the ceramic chunks would affect both flatness and flexibility of the matrix fabric. The only thing that came to mind was if they are very, very small chunks or particles.

I was wondering about the method of manufacture and secondary finishing operation.What alloy compound elements are tolerant enough to withstand the casting process yet still be machineable-?From the photo, I was further wondering about the dimples on the face of the rotor; their purpose and how they were formed.Is this a powder sintered part-?

@JimT: According to the brochure on REL's website, the material can only be machined using diamond tooling.

Heat from braking will cause organic brake pads to off-gas. The idea of a dimpled brake rotor is that the dimples provide space for the gases to expand into, supposedly minimizing brake fade. This is the same idea behind cross-drilled brake rotors. The supposed advantage of dimpled rotors over cross-drilled rotors is that a dimple doesn't reduce the cross-sectional area as much as a drilled hole, so the rotor is less likely to crack. (I say "supposedly" for both of these things because I have heard people dispute both of these claims, and I haven't seen any objective data one way or the other).

It's possible to make MMCs using powder processes, but they are more commonly cast (or, sometimes, cast into billets and then extruded). One way to cast MMCs is by stir casting, in which the reinforcement is stirred into the molten aluminum. Another way is by squeeze casting molten aluminum into a fiber pre-form. Based on the brochure, it looks like this is what REL is doing.

@wb8nbs: The gunmetal gray color of friction ring in the rotor in the picture makes me think that it is probably hardcoat anodized, so it is not just bare aluminum. All other things being equal, I'd expect anodized aluminum to hold up a lot better than bare cast iron. In fact, I'd even expect bare aluminum to hold up better than bare cast iron.

On the other hand, connecting an aluminum brake rotor to a steel wheel hub could be a recipe for galvanic corrosion of the aluminum. Galvanic corrosion between steel hubs and aluminum wheels is also a common problem. In either case, a thick coat of antiseize between the two parts might help to prevent corrosion by galvanically isolating the parts from one another.

Is there any word on the stopping power Vs. heat buildup on these rotors? I recently went from ceramic pads to metallic pads with new rotors all the way around. There was nothing wrong with my old pads except for stress cracks from the heating and cooling cycle.

If the automakers aren't taking a hard look at this, I'd be shocked. Cutting 30 lbs from the weight of a mid-size sedan is a gigantic change. Engineers typically fight to cut a pound or two from their vehicles. If they can cut 10 lbs, they're heroic. Thirty is off the scales.

If the automakers aren't taking a hard look at this, I'd be shocked. Cutting 30 lbs from the weight of a mid-size sedan is a gigantic change. Engineers typically fight to cut a pound or two from their vehicles. If they can cut 10 lbs, they're heroic. Thirty is off the scales.

----------- Sadly this same way of thinking is why they went bankrupt.

------------ We have cost effective composite tech that can drop most car, SUV's weight by 50% and double their mileage. And they know it as they all have built them as showcars like the GM UltraLite. And yet they drool over a few pound savings. Not much critical thinking there.

Reducing car weight is more difficult than it looks. Lighter materials of the same strength are usually more costly. Brake disks are an example where several lighter materials exist, but each currently comes with negatives. Cost for some, limited max temperatures for others. Downsizing is possible and is currently being done, but many buyers stubbornly insist on being able to carry a family in comfort. The best approach seems to be a holistic approach, which is well underway. This, too, is costly, requiring a coordinated design, development, and manufacturing effort with technical support from suppliers. Those efforts are some of the reasons that car weight is not dramatically falling. But progress, though slow, is continuing and new cars now weigh considerably less than some of their forebearers.

I knew a brake job was due a while back and did a little searching as to what race cars use. I knew they would completely fry a steel rotor and formula 1 would melt it. Unfortunatly these seem to be custom built. The only thing I think might be keeping them out of non racing cars is that they don't stop that all that well when braking from low speeds.

I have never had a rotor fail in an automotive disk brake system, but I have had many failures of the caliper mechanism over the years. The reason has been that Chrysler has consistently chosen designs for the caliper assembly that rust and stop sliding where they should. The results have been either brakes that drag and overheat, or brakes that only brake on one side of the disk, resulting in a buildup of an iron oxide material on the inoperative side, which has a much lower friction level, but is far more abrasive to the pads. This failure mode does destry the rotor, but not through any design error in the rotor or material.

The aluminum composite may be a very great improvement, but it would be very handy to find out about it's corrosion resistance to the southeastern Michigans salt brine roadways. If it can stand up to that test, where can we buy these rotors?

I've used aluminum rotors on a race car. I won't ever do it again. The coefficient of thermal expansion is much greater than steel. This means that the rotor heats up and grows, diminishing the clearance between the rotor and caliper until the rotor actually grinds against the caliper (I know, I know... you can always design it with more clearance to compensate. But it is not a drop in replacement at that point). Secondly, Aluminum gets really weak as it gets hot and will fall apart under high mechanical and thermal load. This is exactly what happened to me (lots of little melted aluminum chunks all over the track and my car). Steel, titanium and Carbon can glow red hot and still function as a brake rotor, Aluminum can not.

grand, thanks for your comments. This is not aluminum but an aluminum composite. That fact, plus the fact that the composite includes ceramic, makes me wonder whether one of the reasons for the ceramic is to lower heat, especially since the company developing the material has experience making similar composites for NASA for extreme temperature apps, as they describe here

Obviously we don't run these things right up to the melting point, but this gives us a clear view of how much heat we can dissipate from a material. If I can run a material 3 times hotter, I can make it 3 times smaller.

grand, I'm aware of the fact that this stuff doesn't run as hot as steel, but wanted to make sure you knew it was a composite. The main benefit the research is aimed at here is reducing weight, not size. I'm not surprised to hear that aluminum can be a problem in race cars. The vehicles this material targets are consumer cars and military transport vehicles.

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